Isomerization of paraffins



Patented Dec. 14, 1943 ISOMERIZATION or PAKAFFINS Aristid V. Grosse and Herman Pines, Chicago, Ill.,

assignors to Universal Oil Products Company, Chicago, 111., a corporation of Delaware No Drawing. Application June so, 1939,

Serial No. 282,083

Claims. (01. zoo-683.5)

In amore specific sense the invention is ap- I plicable not only to individual parafiin hydrocarbons of straight chain structure but also to hydrocarbon mixtures containing these compounds in substantial percentages such as straight run gasolines and their fractions, which contain in addition to paraffin hydrocarbons of highly knocking characteristics other hydrocarbons comprising someparafiins of branched chain structure and the usual run of naphthenes and aromatics.

The isomerization of individual normally liquid paraflin hydrocarbons such as normal pentane, and normal hexane is frequently desirable in the manufacture of derivatives since the isomeric compounds are more reactive and, in the case of gasoline or gasoline fractions, the

not available for the neopentane. Similarly, the isomeric hexanes, heptanes, and octanes will show the same progressive relationships as their structure becomes more condensed. As the molecular weight of paraflin hydrocarbons in-' creases, the number of possible and known isomers increases more than arithmetically so that in cases of isomerization involving mixtures of n-paraflins and particularly n-parafiins in admixture with other hydrocarbons in gasolines, the determination of the extent of isomerization is. not possible by analytical methods but can be estimated from the observed change in antiknock value.

In one specific embodiment the present invention comprises treatment of normally liquid parafiin hydrocarbons of straight chain structure with catalysts comprising hydrogen chloride and aluminum chloride on adsorbent supports at temperatures, pressures, and times of contact adequate to efiect substantial isomerization of said hydrocarbons into compounds of more highly branched structure. The process further to be described in more detail in subsequent paragraphs isomerization ha th efleci; of increasing t is applicable not only to individual hydrocarbons antiknock value of the gasolines to a marked extent as will be shown in later examples.

There should be no need for extensively recounting the number of possible isomers of parafiin hydrocarbons since these are all predictable on the present theories of organic chemistry and are well known to'those familiar with this subject. Howeverythe following table is shown to indicate in a general way the change in structure and properties of normal parafiin hydrocarbons and their isomers, particularly since the pentanes constitute some of the lower-boiling constituents of ordinary gasolines.

- yields of the order of -60%. Such yields are or known mixtures of such hydrocarbons, but is also applicable to straight run gasolines which comprise in addition to paraffin hydrocarbons those of cyclic structure including various naphthenes.

We have determined that by theuse of the class of catalysts mentioned, and particularly by the concurrent use ofconsiderable superatmospheric pressures, normally liquid paraflin hydrocarbons of straight chain structure-and particularlythe normal compounds may be converted into hydrocarbons of more highly branched structure with Compound Formula 7 z fi Density 90. n-Pentane. OHa(CH2)aCHa 1.. 36,3 0.6475@0 C 63 on: I V I} i-Pentane onoH1om-.-.'.'-- 28 0.6394 0 0-.-.-- as p om r Ne0-pentane C(CH3)4-; 9L5 o.e'25 1@14.4 0;-

It will be observed from the above that, as the structure of the molecule becomes more compact, boiling point and specific gravity both decrease while the antiknock value as expressed by octane number generally increases'although figures are obtainable at temperatures within the approximate range of 50-250 C. and superatmospheric pressures. Evidently the use of superatmospheric pressures of the order of 1 to 200 and preferably 10 to 200 atmospheres at temperatures of C.-

and higher, besides depressing the volatilization of aluminum chloride catalysts tends also to depress numerous undesirable side reactions which would result in the formation of hydrogen and low molecular weight hydrocarbons, so that the reaction proceeds more or less in one direction until an equilibrium is established.

While inert gases such as nitrogen may be employed in producing the necessary pressure, experiments have shown that it is preferable to employ hydrogen which seems to minimize undesirable side reactions involving decomposition rather than the desired isomerization. As is customary in hydrogenation processes, the hydrogenation reactions are fostered by increase in pressure and in some instances, pressures of 2000 pounds per square inch or higher produce beneficial eifects when the hydrocarbon involved tends to undergo decomposition under the isomerizing conditions.

There are several alternative catalysts consisting of aluminum chloride on inert carrying materials which may be employed in effecting the isomerization reactions characteristic of the process, and while they may be used more or less interchangeably, some are more efiective than others, and it is not intended to infer that they are definitely equivalent. Extensive experiments have indicated that best results are obtained whena minorpercentage of a hydrogen halide is present in the reactions and the necessary amounts of these hydrogen halides are preferably introduced directly in admixture with the hydrocarbons.

One of the desirable features of the present invention is the use of porous granular supports in conjunction with the active aluminum chloride. This facilitates vapor phase operations at temperatures above the sublimation point of aluminum chloride and apparently in some instances seems to lessen the tendency to the formation of sludges consisting of complex addition compounds soflthat the life of the catalyst is extended materially. When granular aluminum chloride sorbedby granular absorbent materials, both of the disadvantages enumerated are to a large extent overcome since the tendency of the chloride to volatilize is partially counteracted by the absorbent action of the supports employed, and

these supports further act to absorb and retain some of the viscous addition compound and prevent the composite catalyst granules from adhering to form large agglomerates.

The general method of preparation of the types of granules whose use in isomerization reactions characterizes the present invention consists in mixing aluminum chloride and a granular supcatalysts resistant to disintegrating influences byusing approximately equal parts by weight of a selected absorbent carbon and anhydrous aluminum chloride. Such proportions, after thorough mechanical mixing, are placed in a pressure vessel, which is preferably made from or lined with suitably corrosion resistant material, a small amount of hydrogen chloride is added, the vessel lytic activity in organic reactions. This procedure is typical of the preparation of any number of similar catalysts using difierent combinations of aluminum chloride on supports already menis employed alone inhydrocarbon ,reactions, it tionedsoon tends toagglomerate on account of the formation'of adhesive sludge-like materials so that violent agitation is necessary to maintain contact of the catalyst with the reacting hydro- The process may be operated under batch or continuous conditions and either in liquid, mixed or vapor-phase as may be desirable or expedient in view of the particular catalyst combination b Among upporting materials which we chosen and the particular hydrocarbon or hydrohave now shown to have practical value as carriers may be mentioned-activated carbon, pumice, various types of fullers earth and clays, particularly those of the montmorillonite or bencarbon mixture undergoing treatment. A simple method of operation consists in adding 5 to 10 per cent of a granular catalyst composite to a treating vessel containing hydrocarbons and protonitetypes, either raw or acid treated, diatoms,- -vided with a mechanical agitating device of some ceous and infusorial earth, kieselguhr; silica-alumina composites,- unglazed porcelain, firebrick, and in general refractory porous substances ,which have substantially no chemical reactivity description. It is best to employ a treater which can be sealed from atmospheric contact and which can be operated under pressure. The solid catalyst is then kept in suspension by moderate with the anhydrous chlorides. It frequently hapso agitation While introducing a s ow str a of hypens that one type of support is better for the aluminum chloride, depending upon the ratio of chloride and support found experimentally to be best for the furtherance of a particular isomerizdrogen chloride, or other hydrogen'halide.

In another type of operation which accelerates the rate of isomerization; the hydrocarbon mixture may be kept at its boiling point by moderate ing reaction so that it is not to be inferred that heating under reflux t ons with the ra the supports can at all times be used interchangeably.

A property of anhydrous aluminum chloride which must be taken into account is its tendlar catalyst maintained in suspension by the ebullition, while the hydrogen halide is'again added in a slow stream. In this type of operation any desired superatmospheric pressure may be emencytosublime atatemperature of approximate- P y o p it h u Of y desired o ly 180 0., so that ii. it'is employed at temperatures above this point it must ordinarily be injected or sublimed into the reaction zone. In the process of the present invention, in which perature. Vapor-phase operations may be conducted by passing vapors of hydrocarbons mixed with a small amount of hydrogen chloride over solid granular catalysts comprising the alumithe aluminum chloride employed is strongly abnum chloride and a selected inert adsorbent action of the granules with water and their cata-' which are contained in treating chambers in the form of granules or pellets.

The following examples are introduced to in,- dicate in a general way the nature of the results obtainable in the operation of the process but they are not 'given with the intention of limiting the scope of the invention in exact correspondence withthe numerical data presented.

Example I The vapors of normal pentane mixed with about 1 per cent by volume of hydrogen chloride were passed through a mass of granular catalyst comprising 1 to mesh particles of activated carbon base supporting about an equal weight of anhydrous aluminum chloride. The temperature employed was 200 C. and a pressure of 450 lbs. per square inch was maintained to depress the volatilization of the aluminum chloride.- The vapors of parts .by weight of normal pentane were passed over parts by weight of the composite catalyst per hour. Fractionation of the products indicated ,that the oncethrough yield of'isopentane was about 27%. by volume of the normal pentane charged. There was produced in addition 3.5% by volume of isobutane and 3.5% by volume of normal butane.

By operatingcontinuously and recycling the unconverted normal compound the final overall yield of isopentane was approximately 80%.

Example II 71 parts by weight of diatomaceous earth was mixed with 29 parts by weight of anhydrous aluminum chloride, and placed in a pressure vessel. 4% by weight of hydrogen chloride gas was introduced and the contents of the vessel were placed under a pressure of 25 atmospheres by the introduction of dry hydrogen. After heating the vessel for a period of three hours at a temperature of approximately 250 C. during agitation, it was found that the aluminum chloride was exactly adsorbed on the diatomaceous earth so that an apparently dry material was formed.

Normal pentane vapors containing about 2% by weight of. hydrogen chloride was passed through the catalyst at a temperature of 190 C.

and a pressure of 400 lbs. per square inch. There was produced about 25% by volume of iso-pentane, based on the volume of normal pentane charged as a once-through yield. Some side reactions occurred as indicated by the presence of about 5% by volume of lower and 5% by volume of higher boiling hydrocarbons. In recycle operation, the ultimateyield of iso-pentane was approximately 70%.

Example III ed with 18 parts by weight of aluminum chloride at a temperature of 260 C. under a hydrogen pressure of 30 atmospheres in the presence of 4% by weight of hydrogen chloride gas. After four hours heating the particles of the porcelain were dry, and were utilizable in the isomerization of normal pentane in substantially the same manner and with approximately equivalent results to those shown in the three preceding examples.

Example V Example VI Using another portion of the same catalyst employed in Example II, normal pentane was isomerized under the conditions specified in Example V. The weight per cent yield of iso-pentane was 84.5 and there wasalso produced 5.4%

of propane, 4.5% of butane, and 5.6% of residual normal pentane. This indicates a highly selective isomerization reaction.

Example VII included 6.7% propane, 5.3% of butanes, and

This

22.6% of unconverted normal pentane. again indicates an extremely selective isomerization reaction.

Example VIII Normal pentane was continuously isomerized by passing its vapors mixed with 15% hydrogen chloride by volume over an aluminum chloridepumice catalyst at a temperature of 150 C. under a hydrogen pressure of 2000 lbs. per square inch and a liquid space velocity of 0.75. The

average composition of the exit gases in a run of several hours duration was iso-pentane, 22%; normal pentane, 77.1%; and less than 1% of side reactions.

Example IX erized as in Example VIII using an aluminum parts by weight of pumice was mixed with 32 parts of substantially anhydrous aluminum chloride and heated in a pressure vessel at 250 C. under 25 atmospheres of hydrogen pressure in the presence of 45% by weight of hydrogen chloride gas as in the two preceding examples.

The vapors of normal pentane containing approximately 2% by weight of hydrogen chloride were passed over the above catalyst at a temperature of 180 C. under a pressure of 400 lbs. per square inch. In a once-through run, the yield of iso-pentane was approximately 20% and this was increased to anultimate yield of 65% by recycling operations.

lain sized to approximately 1-20 mesh were heatchloride-kieselguhr catalyst. By passing the vapors mixed with 5% by volume of hydrogen chloride over the catalyst at a temperature of 0., a hydrogen pressure of 122 pounds per square inch, and a liquid space velocity of 0.75. The average composition of the products in a run of several hours duration was iso-pentane', 45.3%; propane, 1.2%; butanes, 0.9%; and unconverted normal pentane, 52.6%.

We claim as our invention:

1 A process for increasing the anti-knock properties of normally liquid hydrocarbon fractions boiling in the gasoline range and containing parafiins of relatively low anti-knock value. 'which comprises subjecting the hydrocarbon fraction under isomerizing conditions of temperature, pressure and time to .the action of aluminum chloride in the presence of added hydrogen chloride, correlating the amount of hy-,

drogen chloride and said isomerizing conditions of temperature, pressure and time to convert a substantial portion of the parafilns contained in said fraction into isomers thereof having the same molecular weight as and of higher antiknock properties than said paraflins, and recovering the treated hydrocarbon fraction containing said parafiin isomers.

2. A process for increasing the anti-knock properties of normally liquid hydrocarbon fractions boiling in the gasoline range and containing normal paraflins of less than seven carbon atoms to the molecule, which comprises subjecting the hydrocarbon fraction under isomerizing conditions of temperature, pressure and time to the action of aluminum chloride in the presence.

of added hydrogen chloride, correlating the amount of hydrogen chloride and said isomerizing conditions of temperature, pressure and time to convert a substantial portion of said normal paraffins into branched chain paraflins of the same molecular weight, and recovering the treated hydrocarbon fraction containing said branched chain paraflins.

3. A process for isomerizing a normally liquid paraffin hydrocarbon boiling in the gasoline range, which comprises subjecting said paraffin under isomerizing conditions of temperature,

pressure and time to the action of aluminum chloride in the presence of added hydrogen chloride, correlating the amount of hydrogen chloride and said isomerizing conditions of temperature, pressure and time to convert a substantial portion of said paraffin into an isomer or isomers thereof having the same molecular weight as said paraifin, and recovering the resulting product containing said parafiin isomer or isomers.

4. A process for isomerizing a normally liquid parafiin hydrocarbon boiling in the gasoline range, which comprises subjecting said paraflln under isomerizing conditions of temperature, pressure and time to the action of aluminum chloride in the presence of added hydrogen chloride, said temperature being in the approximate range of 50 to 250 C., correlating the amount of hydrogen chloride and said isomerizing conditions of temperature, pressure and time to effect, as the principal reaction in the process, the conversion of a substantial portion of said paraffin into'an isomer or isomers thereof having the same molecular weight as said parafiin, and recovering the resulting product containing said paraffin isomer or isomers.

5. A process for isomerizing a normally liquid par'aflin hydrocarbon boiling in the gasoline range, which comprises subjecting said paraffin under isomerizing conditions of temperature,

pressure and time to the action of aluminum 

